The present invention relates to devices for coding audio signals, intended especially to be deployed in applications concerning the transmission or storage of digitized and compressed audio signals.
The invention pertains more precisely to the quantization modules included in these audio coding devices.
The invention relates more particularly to 3D sound scene coding. A 3D sound scene, also called surround sound, comprises a plurality of audio channels each corresponding to monophonic signals.
A technique for coding signals of a sound scene used in the “MPEG Audio Surround” coder (cf. “Text of ISO/IEC FDIS 23003-1, MPEG Surround”, ISO/IEC JTC1/SC29/WG11 N8324, Jul. 2006, Klagenfurt, Austria), comprises the extraction and coding of spatial parameters on the basis of the whole set of monophonic audio signals on the various channels. These signals are thereafter mixed to obtain a monophonic or stereophonic signal, which is then compressed by a conventional mono or stereo coder (for example of the MPEG-4 AAC, HE-AAC type, etc). At the decoder level, the synthesis of the reconstructed 3D sound scene is done on the basis of the spatial parameters and the decoded mono or stereo signal.
The coding of the multichannel signals requires in certain cases the introduction of a transformation (KLT, Ambisonic, DCT, etc.) making it possible to take better account of the interactions which may exist between the various signals of the sound scene to be coded.
It is always necessary to increase the audio quality of the sound scenes reconstructed after a coding and decoding operation.